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larly the engine need be run only about an hour each time. But if the owner should not be in possession of an hydrometer, it is better to run the engine for 2 or 3 hours each time, for the sake of safety. To charge the battery properly the engine should be run at a speed corresponding to a car speed of about 20 mph on the direct drive. There may be cases, however, where the owner is compelled to store his car in a space where it is practically impossible to run the engine. Where this is the case, it is recommended, if electric current is available, that the owner purchase a rectifier or small charging machine. A charge over night, or for about 12 hours, every 2 weeks with this apparatus will be sufficient to keep the battery in a healthy condition. Before beginning the charging the battery should be inspected to see if it is filled with solution. If the solution needs replenishing, distilled water should be added until the solution fully covers the plates, which may be determined by removing the vent plugs and looking down into the cells. In case it is impossible to run the engine for charging and the owner does not care to incur the expense of purchasing a rectifier, he should remove the battery from the car and arrange for its storage at a garage which has charging facilities, stipulating that it must be charged every 2 weeks. The cost of having it so cared for will be nominal and will prove excellent insurance against deterioration.

To care for storage batteries of a type that is easily taken apart the following method is recommended: First charge the battery until every cell is in a state of complete charge. If there should be any short circuited cells they should be put into condition before the charge is commenced, so that they will receive the full benefit of the charge. Then remove the elements from the jars, separating the positive from the negative groups, and place in water for about 1 hour to dissolve out any electrolyte adhering to the plates. Then withdraw the groups and allow them to drain and dry. The positives when dry are ready to be put away. If the negatives in drying become hot enough to steam, they should be rinsed or sprinkled again with clean water and then allowed to dry thoroughly. When dry, the negatives should be replaced in the electrolyte (of from 1.275 to 1.300 specific gravity), care being taken to immerse them completely and allow them to soak for 3 or 4 hours. Two groups may be placed in a jar and the jar filled with electrolyte. After rinsing and drying the plates are ready to be put away.

The rubber separators should be rinsed in water. Wood separators after having been in service, will not stand much handling and had better be thrown away. If it is thought worth while to keep them they must be immersed in water or weak electrolyte, and in reassembling the electrolyte must be put into the cells immediately, as wet wood separators must not stand exposed to the air for any unnecessary moment, especially when in contact with plates. Storage batteries always should be stored in a dry place, preferably in one where the temperature will never fall below 40° Fahr. Storage battery solution or electrolyte varies greatly in density between the points of complete charge and complete discharge. When completely discharged the electrolyte of the average battery has a specific gravity of 1.14, and a sulphuric acid solution of 1.14 specific gravity has a freezing point of about 10° Fahr. Therefore, if a completely discharged battery is allowed to stand where it is exposed to extremely low temperature it is quite possible for the electrolyte to freeze and the cells to be injured in consequence. However, as already pointed out, a battery for other reasons must not be allowed to stand in the discharged condition for any length of time. With increasirg charge the density of the electrolyte increases until, when the charge is complete, it attains 1.28 specific gravity. The freezing temperature of the solution drops very quickly as the specific gravity increases, somewhat as follows: Spec. Grav.

Freez. Point Degrees 1.14

+10 1.16

+ 5 1.175

4 1.20

-16 1.225

-36 1.25

-60 1.28

-85

Consequently there is no possibility of a storage battery being injured by freezing in this latitude if it is kept in a fair state of charge.

Spark Plug Faults. The part of the ignition system that is apt to give the most trouble, and for the most part through no fault of its own, is the spark plug which is placed in the combustion chamber in order to permit a spark to take place between the electrodes whenever it is necessary to explode a charge of gas.

Spark plug troubles are not hard to locate, as they may be readily determined on inspection. If an engine misses fire, i.e., runs irregularly, it is necessary to locate the spark plug at fault in order to remove it for inspection or cleaning. The common method of doing this is to short circuit the spark plug terminal with some metallic portion of the engine by using a wood handle screw driver, as shown at Fig. 82, A. Each plug is tried in turn, and when a good one is short circuited the engine will run even slower than before. If a plug is short circuited and the engine does not run any slower or work differently, one may assume that the plug is defective or that the cylinder is not firing for some other reason. A very simple spark plug tester which can be made by any repairman for use on cars employing magneto ignition or high-tension battery-distributor ignition, is shown at Fig. 82, B. This consists of two strips of brass riveted together at one end and fitted into a fiber or hard rubber handle. The brass strips are spread apart so that contact may be made between the plug body and insulated central terminal of practically any size plug. When a four-cylinder or six-cylinder engine uses individual spark coils for ignition, it is possible to detect the missing cylinder by holding down the coil vibrators with the fingers, leaving the engine to run on one of the coil units or one cylinder as the others are cut out. Each coil unit is tried in turn, and when all others are rendered inoperative except the defective one or the coil leading to the defective spark plug, the engine will stop. The wire leading from the spark coil is traced to the spark plug, and that member removed for examination. The common trouble is a deposit of burnt oil or carbon around the insulator and between the plug points. This short circuits the current as it provides an easier path for

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Fig. 82.- Showing Methods of Testing Spark Plug and Adjusting Air

Gap Between the Electrodes.

the passage of electricity than the air gap does. If the points are too close together the plug will become short circuited very quickly and ignition is apt to be erratic because the spark does not have sufficient heat to ignite the mixture. If the spark points are too far apart the resistance is apt to be too great for the current to jump the air gap. The porcelain may crack or become broken, in which case the current is apt to short circuit if the break is down in the plug body. If a mica or lava insulator becomes oil soaked, this also will produce short circuit.

Most plugs are of the easily separable form, as shown at Fig. 82, A, in which case the insulator may be easily removed by unscrewing the packing nuts that keep it seated against the plug body. If the plug is clean when examined the thing to do is to see that the spark gap is correct. This should be about onethirty-second inch. Whenever a spark plug is to be put into use, whether it is a new one or old one which has been cleaned, the spark points should always be set so there is a gap of about the thickness of a smooth ten-cent piece between them. The method of obtaining a correct spark gap depends entirely upon the type of the plug. In the plug shown at Fig. 82, C, which has a plate at the end, it is necessary to bend over the center stem by using a small screw driver or similar tool as indicated. With a plug of the form shown at D the center stem is bent the proper distance away from the small hook-shaped wire or electrode which projects from the bottom of the spark plug body. In some plugs it is easier to bend the central stem than the side electrode, as the latter is of hard material, whereas in others it is not possible to bend the central electrode and the point attached to the plug body must be bent instead. It is important when replacing the por. celain insulator after cleaning to make sure that the packing nut is drawn down quite tight in order that the joint will be tight enough to hold the explosion pressure. It is also necessary to screw down the small hexagon lock nut on top of the spark plug porcelain, as if this is left loose the center stem of the plug will be free to turn in the porcelain, especially if the thumb nut or terminal is being tightened. It will be apparent that if the center stem is bent over toward the side electrode in the manner shown at D, that if it is turned a very small part of a circle the size of the gap between the center stem and side electrode will be altered appreciably. If the porcelain is found covered with oil and car

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